The present invention relates to a rubber composition which comprises a blend of epichlorohydrin-propylene oxide type copolymer rubber and chloroprene rubber, and has remarkably improved properties.
Among known oil-resistant rubber products, particularly chloroprene rubber (hereinafter referred to as CR) is known to have properties which are advantageously balanced and, as such, has been widely used for such as hose-covers, dust cover boots, belts and so forth in automobiles: CR has been put for use in view of its remarkable properties with respect to such as the oil resistance, the heat resistance, the low-temperature resistance, the ozone resistance, the resistance to bending and so on.
However, as the social demand for controlling the pollution of air has of late grown to be greater and, to cope with this, the control of exhaust gas from passenger cars has become more strongly regulated than before, there have been various improvements made in or relating to for example automobile engines. A result of this is that it is now required of CR to have a further improved heat resistance. However, CR can hardly answer such demand for a further improvement in its heat resistance, and since it is prone to undergo a curing-type deterioration and can hardly stand a long use, it is likely to give rise to a serious danger. Also, CR has a crystalline structure and is regarded as being unsuited for use in cold areas, and it in addition involves a problem with respect to the dynamic ozone proof.
Then, with epichlorohydrin-ethylene oxide copolymer rubber (hereinafter referred to as CHC), although this has exceeding properties in comparison to CR, with respect to the heat resistance, oil resistance, low-temperature resistance and dynamic ozone resistance, it fails to be satisfactory with respect to the resistance to bending and it is not suitable for use as material which is required to possess high dynamic characteristics.
With epichlorohydrin-propylene oxide type copolymer rubber, then, while it exceeds CR in respect of the heat resistance, oil resistance, low-temperature resistance and dynamic ozone resistance, it fails to be comparable to CR in respect of the flexibility.